JPH09227941A - Production of grain oriented silicon steel sheet excellent in magnetic property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a grain oriented silicon steel sheet extremely excellent in magnetic properties by executing cooling by a specified method from hot rolled sheet annealing for a slab contg. specified weight ratios of specified components. SOLUTION: A slab contg., by weight, 0.021 to 0.O75% C, 2.5 to 4.5% Si, 0.010 to 0.060% acid soluble Al, 0.0010 to 0.0130% N, <=0.4% S+0.405Se, 0.05 to 0.8% Mn, and the balance Fe with inevitable impurities is heated at <1280 deg.C, is thereafter hot rolled and is subjected to hot rolled sheet annealing. Successively, it is subjected to final cold rolling, is next subjected to decarburizing annealing to regulate the grain size of primarily recrystallized grains to 18 to 35μm, and after that, finish annealing is executed. As for the above hot rolled sheet annealing, in the cooling stage, it is cooled at <=10 deg.C/sec from 900 to 700 deg.C and is cooled at >=10 deg.C/sec from 700 to 200 deg.C, by which AlN as an inhibitor is finely precipitated after the hot rolled sheet annealing to produce the grain oriented silicon steel sheet excellent in magnetic properties.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties by controlling the average primary recrystallization grain size.

[0002]

2. Description of the Related Art The unidirectional electrical steel sheets that have been put into practical use at present have a sharp texture formed by secondary recrystallization without exception. The secondary recrystallization texture is controlled to a crystal orientation that gives the best performance and efficiency when the steel sheet is used as electrical equipment. Therefore, the higher the sharpness of the secondary recrystallization texture, the better the performance of the electric device. The sharpness of the secondary recrystallization texture generally strongly reflects on the magnetic flux density B ₈ (the strength of the magnetic flux density in a magnetic field of 800 AT / m). The magnetic flux density changes very sensitively due to the secondary recrystallized texture. Therefore, proper secondary recrystallization growth is beneficial to manufacturers and users.

The secondary recrystallization is an abnormal grain growth phenomenon of the primary recrystallized grains having extremely strong orientation selectivity. The main factor controlling the magnetic flux density, which is an index of the degree of {110} <001> orientation integration of the secondary recrystallized grains, is the texture of the primary recrystallized structure,
It is already well recognized that they are the crystal grain size and the inhibitor strength (resistance to the grain boundary migration due to the precipitate boundary segregation element).

In hot-rolled sheet annealing, a primary soaking temperature, a secondary soaking temperature and a cooling temperature are set in order to control the primary recrystallization texture. In Japanese Unexamined Patent Publication (Kokai) No. 5-125446, the primary soaking temperature T1 is set to be in the range of 1150 to 950 ° C., and after soaking at this temperature for 180 seconds, it stays on the low temperature side at 750 to 900 ° C. for 30 seconds or more and 300 seconds or less. Then, a method of cooling to room temperature at a rate of 10 ° C./sec or more is presented (FIG. 1a, Table 1A). Also, fairness 7
-74386 gazette, primary soaking temperature 900-1080
After soaking within 180 seconds at ℃, secondary soaking temperature 750-9
It proposes a method of holding at 00 ° C for 30 seconds to 300 seconds and then cooling to room temperature at a rate of 10 ° C / sec or more (Fig. 1b, Table 1B). As described above, the cooling start temperature so far is mostly from the two-phase coexistence region of 700 ° C. or higher, and there is no cooling from the temperature of lower than that.

[0005]

As described above, the cooling start temperature after the hot-rolled sheet annealing up to now is mostly from the two-phase coexistence region of 700 ° C. or higher, and therefore AlN is miniaturized. However, it cannot be said that they are always uniform,
As a result, the magnetic properties fluctuated, and it was difficult to manufacture the intended grain-oriented electrical steel sheet having high magnetic properties.

[0006]

In order to solve the above-mentioned problems, the present invention is to precipitate uniformed fine AlN by appropriately controlling the cooling in the cooling process after hot-rolled sheet annealing. , Its gist is as follows. In the present invention, the weight ratio of C: 0.021 to 0.075, Si: 2.
5 to 4.5%, acid-soluble Al: 0.010 to 0.060
%, N: 0.0010 to 0.0130%, S + 0.40
5Se: 0.4% or less, Mn: 0.05 to 0.8%, the balance slab consisting of Fe and unavoidable impurities at 1280 ° C.
After heating at a temperature of less than, hot rolled, subjected to hot rolled sheet annealing,
Subsequently, including final cold rolling with a rolling reduction of 80% or more, if necessary, cold rolling is performed once or more with intermediate annealing sandwiched, and then decarburization annealing, and the particle size of primary recrystallization is set to 18 to 35 μm,
In the method for producing a unidirectional electrical steel sheet in which nitriding is performed, an annealing separator is applied, and finish annealing is performed, cooling is performed at 10 ° C / sec or more between 700 and 200 ° C in the cooling process of the hot rolled sheet annealing. , AlN as an inhibitor after the hot rolled sheet annealing is finely precipitated, and 900 to 7 in the cooling process of the hot rolled sheet annealing.
Provided is a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, which comprises cooling between 00 ° C at 10 ° C / sec or less.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. In the present invention, the reasons for limiting the composition of the electrical steel slab as a starting material will be described below. When C is less than 0.021%, the secondary recrystallization becomes unstable, and the magnetic flux density (B ₈ value) of the product becomes low even below 1.80 T even when the secondary recrystallization is performed. On the other hand, if the content of C exceeds 0.075% and becomes too large, the decarburization annealing time becomes long and the productivity is remarkably impaired.

If the Si content is less than 2.5%, it is difficult to obtain a product having a low iron loss. On the other hand, if the Si content exceeds 4.5%, cracks and fractures frequently occur during cold rolling of the material, which is stable. Cannot perform cold rolling work. Al combines with N to form AlN, but in the present invention, it is essential to form (Al, Si) N by nitriding the steel sheet in a subsequent step, that is, after completion of primary recrystallization. Free Al must be above a certain level. Therefore, as acid-soluble Al, 0.0
10 to 0.060% is added.

N must be 0.013% or less.
If it exceeds this, swelling of the steel sheet surface called a plister occurs. Also, it becomes difficult to adjust the primary recrystallization structure. The lower limit is preferably 0.0010%. Below this value, it becomes difficult to develop secondary recrystallization. If Mn is too small, secondary recrystallization becomes unstable, and if it is too large, a product having a high magnetic flux density cannot be obtained. The proper content is 0.05-
0.8%.

The inclusion of a trace amount of Cu, P, Ti, Bi in steel does not impair the gist of the present invention.
Next, the manufacturing process of the present invention will be described. The electromagnetic steel slab can be obtained by melting steel in a melting furnace such as a converter or an electric furnace, subjecting it to vacuum degassing treatment if necessary, and then performing continuous casting or ingot casting and slab rolling.

After that, slab heating is performed prior to hot rolling. In the process of the present invention, the heating temperature of the slab is set to 1280 ° C. or lower, the consumption of heating energy is reduced, and AlN in the steel is not completely solid-solved to be an incomplete solid solution state. At this temperature, MnS having a higher solid solution state is naturally in an incomplete solid solution state.

As a result of various studies on the primary and secondary soaking times, the primary soaking time is preferably 180 seconds or less, and the secondary soaking temperature residence time is preferably 300 seconds or less. Further, when the cooling rate from the secondary soaking temperature range is 10 ° C./sec or more, high B ₈ can be stably obtained. A faster cooling temperature is preferable because it promotes fine precipitation of carbides and nitrides, but this condition is satisfied because of the mechanical capacity of the manufacturing equipment. In addition, this is applicable also to the annealing performed after a hot rolled sheet is pickled and cold rolled.

The reason why high B ₈ can be obtained by this annealing has not been clarified yet, but at present it is considered as follows. Factors that influence the secondary recrystallization phenomenon, including the orientation of secondary recrystallization, include primary recrystallization texture (average grain size, grain size distribution), texture, and inhibitor strength. After the completion of primary recrystallization, the texture and the grain size distribution change with the grain growth. In order to facilitate the nucleation and grain growth of the secondary recrystallization, it is desirable that each grain size of the primary recrystallization be uniform and have a certain size or more.

On the other hand, the texture is preferably oriented grains that undergo secondary recrystallization ({110} <001> orientation, etc.) and oriented grains ({111} <112> orientation, etc.) that facilitate secondary recrystallized grain growth. It is necessary to get the amount. The crystal grain size (recrystallization rate) and the amount of transformation phase before cold rolling excluding the rolling rate,
Solid solution C and the like have an effect. In the process of the present invention, the presence of the inhibitor before cold rolling is not preferable because it makes it difficult to adjust the primary recrystallization structure, but precipitation of AlN is unavoidable as long as Al and N are used as the material components. In particular, it is important to control fine precipitates that affect grain growth. Under the same annealing condition, a material having a low Al (AlR) has a strong primary recrystallized grain growth suppressing power due to the refinement of the precipitation size. The reason why the primary soaking temperature in hot-rolled sheet annealing is changed by AlR is that the precipitation size of AlN caused by the difference in AlR amount is controlled by the hot-rolled sheet annealing temperature to eliminate the fluctuation of primary recrystallized grain growth and to make it uniform and constant. Is to obtain a primary recrystallized structure with a grain size equal to or larger than.

The optimization of the secondary soaking temperature and the texture can be achieved in combination with the decarburization annealing temperature performed after cold rolling. Cold rolling is 80% or more in order to obtain high B ₈ . In addition to decarburization, decarburization annealing has a role of adjusting the primary recrystallization structure and forming an oxide layer necessary for forming a film as described above, which is normally wet hydrogen and nitrogen in the temperature range of 800 to 900 ° C. It is performed in a mixed gas of gases. The atmosphere gas is a mixture of hydrogen and nitrogen, and the dew point is preferably 30 ° C. or higher.

After decarburization annealing, a chemical agent having a nitriding ability, for example, M
After applying an annealing separator containing MgO and TiO ₂ added with nN, CrN, etc., finish annealing is performed at a temperature of 1100 ° C. or higher. Further, a gas having a nitriding ability may be used as an atmosphere gas for the finish annealing. As another implementation, N after decarburization annealing
700 ~ in an atmosphere containing a gas with nitriding ability such as H ₃
It is also possible to perform short-time annealing at a temperature of 800 ° C. for nitriding, and then apply a known annealing separator to finish annealing.

As can be seen from FIG. 2, the precipitates formed near the grain boundaries are different. We believe that this difference is the cause of good magnetic properties. That is, when the hot rolled sheet is annealed under the conditions of the present invention, the formation of carbides after cold rolling is different, and the solid solution C and N are fixed to defects such as dislocations formed by cold rolling due to the subsequent pass aging. It is considered that the deformation mechanism is influenced by the action of the action, or the action of suppressing the dislocation motion due to the fine carbide and the fine nitride, to give good magnetic properties.

An example will be described below.

[0019]

【Example】

<Example 1> C: 0.053%, Si: 3.25%, M
n: 0.094%, P: 0.025%, S: 0.007
%, Al: 0.029%, N: 0.0078%, Cr:
A steel ingot containing 0.12% and Sn: 0.05% was produced and hot-rolled into a hot-rolled sheet having a thickness of 2.3 mm. After this, hot-rolled sheet annealing is held at a temperature of 1120 ° C. for a time of 30 s, and then a temperature of 900
After holding at 30 ℃ for 30s, 5 ℃ between 900-700 ℃
/ S, and then rapidly cooled at 400 ° C / s by cooling in a water bath at 700 ° C to 0 ° C (Fig. 1a, Table 1 Example 1).

After this, pickling and cold rolling to 0.22 mm,
Then, decarburization annealing at 820 to 840 ° C for 90 seconds is performed to a dew point of 62.
It was carried out in an atmosphere of wet hydrogen and nitrogen at ℃. Subsequently, the nitriding treatment was performed at 750 ° C. for 30 seconds in an atmosphere gas in which ammonia was added to a dry nitrogen / hydrogen mixture gas, and the [N] content of the steel sheet after nitriding was set to 200 ppm. After this, MgO and TiO ₂
After applying and drying the slurry whose main component is 1200 ° C
A 20-hour finish annealing was performed.

From this result, high B ₈ was obtained under the condition of being rapidly cooled from 700 ° C. (FIG. 3, Table 2 and Table 3). This satisfies the conditions of the present invention. <Example 2> Hot rolled sheet annealing was performed under the following conditions with the same components and the same steps as in Example 1. Temperature 1120 ℃, 30
After being held at s, it was gradually cooled at 5 ° C / s between 1120 and 700 ° C, and then rapidly cooled below 700 ° C at 400 ° C / s (Fig. 1b, Table 1 Example 2).

From these results, high B ₈ was obtained under the condition of being rapidly cooled from 700 ° C. (FIG. 4, Table 2 and Table 3). This satisfies the conditions of the present invention.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3]

[0026]

As described above, by carrying out the cooling from the hot rolled sheet annealing described in the present invention, it is possible to obtain a unidirectional electrical steel sheet having extremely excellent magnetic properties.

[Brief description of drawings]

FIG. 1 shows a hot rolled sheet annealing cycle and a cooling method after hot rolled sheet annealing, and is a diagram showing a conventional cooling method and a cooling control method of the present invention.

FIG. 2 is a photograph of a crystal structure by a cooling method after hot-rolled sheet annealing, and (a) is a photograph of a crystal structure by a conventional cooling method.
(B) is a photograph of the crystal structure by the cooling method of the present invention.

FIG. 3 is a diagram showing a comparison of magnetic flux density between a conventional cooling method and a cooling method according to the present invention in a cooling method after hot-rolled sheet annealing.

FIG. 4 is a diagram showing comparison of magnetic flux densities between a conventional cooling method and a cooling method according to the present invention under different conditions in a cooling method after annealing a hot rolled sheet.

Claims (1)

[Claims] 1. A weight ratio of C: 0.021 to 0.075,
Si: 2.5-4.5%, acid-soluble Al: 0.010-
0.060%, N: 0.0010 to 0.0130%, S
+0.405 Se: 0.4% or less, Mn: 0.05 to
After heating a slab consisting of 0.8% and the balance being Fe and unavoidable impurities at a temperature of less than 1280 ° C., hot rolling, hot-rolled sheet annealing, and subsequent final cold rolling with a rolling reduction of 80% or more, If necessary, cold rolling is performed once or more with an intermediate anneal sandwiched between them, followed by decarburization anneal to obtain a primary recrystallization grain size of 18 to 35.
In the method for producing a unidirectional electrical steel sheet in which nitriding is performed, an annealing separator is applied, and finish annealing is performed after the thickness is adjusted to μm, a temperature of 900 ° C. to 700 ° C. in the cooling process of the hot rolled sheet annealing is 10 ° C. /
Cool at less than sec, 700 ℃ to 200 ℃, 10 ℃ / sec
A method for producing a grain-oriented electrical steel sheet having excellent magnetic characteristics, which comprises finely precipitating AlN as an inhibitor after hot-rolled sheet annealing by cooling as described above.